Trying out media blasting at home, slag hardness/grit?
08-19-2012, 03:35 PM
#1
Three Wheelin'
Thread Starter
A media blasting thread, share your successes with blasting
Update: I tried blasting my cam covers at our college blasting cabinet. The media was walnut shells. I played around with flow and found 90PSI worked the best. However, walnut shells seem to be way too soft to remove the coating. I have a video of doing it.
As you can see, it didn't work very well. I know most of this was due to the media being too soft. However, the gun (it is a siphon feed system) clogged up so often. The siphon feed had a cup on the end and a removed this cup to see if i could get more media to flow out of the nozzle and it was a little better. Probably going to just pay to get them sandblasted. Here at the college they only use environmentally friendly abrasives. We can use soda as well but at the time the blaster was on it was configured to just use walnut shells. Soda would require switching to a hopper system which would require hooking up a bunch of hoses and the collector system.
As you can see, it didn't work very well. I know most of this was due to the media being too soft. However, the gun (it is a siphon feed system) clogged up so often. The siphon feed had a cup on the end and a removed this cup to see if i could get more media to flow out of the nozzle and it was a little better. Probably going to just pay to get them sandblasted. Here at the college they only use environmentally friendly abrasives. We can use soda as well but at the time the blaster was on it was configured to just use walnut shells. Soda would require switching to a hopper system which would require hooking up a bunch of hoses and the collector system.
Last edited by 17prospective buyer; 08-24-2012 at 09:57 AM.
08-19-2012, 03:52 PM
#2
Drifting
I seriously doubt you will be able to do much of anything with a 10 gallon tank even with 4 cfm. Media blasting is even more a job for a compressor that painting a car. You will be spending most of your time waiting on the tank to refill. Find a used 65 gallon in your local Craigslist. I played around with smaller compressors for awhile and until you get a good reserve size tank its mostly a waste of time.
I have a gravity feed blaster as well and I find I have to use one hand to shake the blaster to keep media flowing. You can do it but its a pain...and slow go for sure. Maybe I was doing something wrong as I would LOVE to use it more often.
I have also learned that you can use any media you want but you may need to adjust the distance your gun tip is from your work. I had my bumpers SAND blasted by a pro and it did a great job. However I watched him do it and he had a good 18" between the gun tip and the bumper surface.
I have a gravity feed blaster as well and I find I have to use one hand to shake the blaster to keep media flowing. You can do it but its a pain...and slow go for sure. Maybe I was doing something wrong as I would LOVE to use it more often.
I have also learned that you can use any media you want but you may need to adjust the distance your gun tip is from your work. I had my bumpers SAND blasted by a pro and it did a great job. However I watched him do it and he had a good 18" between the gun tip and the bumper surface.
08-19-2012, 04:31 PM
#3
Three Wheelin'
Thread Starter
I know capacity is one of the keys to getting it done with a home blasting setup. Maybe i will look for a tank to further expand capacity. 65 gallons is awful big. How much capacity do you run? Can you recommend an air pump for it as well? I know you can use a small air pump but filling a huge tank up will probably be way over the rated duty cycle for the compressor, not to mention the oil consumption.
Princess Auto also has separate piston air pumps for sale, i think they're for heavy needs since they have a big flywheel pully to drive it with an electric motor.
Can you compensate for lack of flow by using harder media?
What about getting an old junker 4 banger engine that seals and using that as a big compressor?? Would work with some check valves no? I do mean powering it via an electric motor and sealing it up to be like a big air pump.
Princess Auto also has separate piston air pumps for sale, i think they're for heavy needs since they have a big flywheel pully to drive it with an electric motor.
Can you compensate for lack of flow by using harder media?
What about getting an old junker 4 banger engine that seals and using that as a big compressor?? Would work with some check valves no? I do mean powering it via an electric motor and sealing it up to be like a big air pump.
08-19-2012, 05:41 PM
#4
Rennlist Member
Most of my experience is with glass beads. There is no substitute for CFM. Increased PSI will give the illusion of getting more from glass beads but will break the beads faster and you’ll be shooting powder to no avail. I doubt you’ accomplish much with baking soda but I don’t know your goal. Increasing PSI may help with slag but higher PSI will deplete your volume sooner. Again, there is no substitute for CFM (at PSI).
As far as driving a 4 banger with an electric motor, if you’ve got a scrap yard with good parts and a lot of time, I say go for it and good luck. You’d be better off using a V8 running on 4 and 4 pumping air.
Or, as Dean said, keep an eye on CL for a good used proper compressor.
Cheers,
Denny
As far as driving a 4 banger with an electric motor, if you’ve got a scrap yard with good parts and a lot of time, I say go for it and good luck. You’d be better off using a V8 running on 4 and 4 pumping air.
Or, as Dean said, keep an eye on CL for a good used proper compressor.
Cheers,
Denny
Last edited by depami; 08-20-2012 at 01:07 AM.
08-19-2012, 05:41 PM
#5
Drifting
Most all air tools require 90 to 100 PSI. If you have a garage a standing 65 gallon compressor only takes up I would say 6 square feet. It has been the best tool I have purchased in years. Keep an eye on Craigslist for one. People move all the time and can't or don't want to take it with them. I have seen usable compressors go for $250...just be ready. The larger ones run on 220 Volts. What I did is I made my own extension cord and put a electric dryer plug on it. When I use it I just plug it into the dryer outlet. The larger 220 volt motors run a lot quieter than the 110 motors. Those scream.
Back to the media. You can us a harder media at a greater distance ( maybe a lower pressure too) but I suggest LOTS of practice on something you don't care about. It all takes a certain amount of touch to do right. Too slow or too close and you rip holes in things or pit aluminum...too far away or too fast and your wasting your time.
Its always CHANCY using a media that more aggressive than you need. The SAFE thing is to use whats suggested. All I am saying is with practice and patience...you can use most anything thats handy and available. Some will disagree I know..but I have seen sand used on soft bumpers and it did a great job.
Back to the media. You can us a harder media at a greater distance ( maybe a lower pressure too) but I suggest LOTS of practice on something you don't care about. It all takes a certain amount of touch to do right. Too slow or too close and you rip holes in things or pit aluminum...too far away or too fast and your wasting your time.
Its always CHANCY using a media that more aggressive than you need. The SAFE thing is to use whats suggested. All I am saying is with practice and patience...you can use most anything thats handy and available. Some will disagree I know..but I have seen sand used on soft bumpers and it did a great job.
Last edited by Dean_Fuller; 08-19-2012 at 05:59 PM.
08-19-2012, 09:25 PM
#6
Three Wheelin'
Thread Starter
Dean and Depami, thanks for your inputs. I will search Kijiji for a compressor setup. Should i be looking for a two stage 220V unit? The price point seems to go up exponentially if you want a 2 stage or 3 stage.
Nonetheless, i will try with my small setup and see how it progresses. It would make stripping parts for paint much easier. Maybe if i can convince my parents that they would have uses for it as well then i could get them on board with getting some more capacity.
Nonetheless, i will try with my small setup and see how it progresses. It would make stripping parts for paint much easier. Maybe if i can convince my parents that they would have uses for it as well then i could get them on board with getting some more capacity.
08-20-2012, 12:36 AM
#7
Rennlist Member
Rennlist Site Sponsor
Back in the day, it was common to make a compressor from a small six-cylinder auto engine. I never did it, but my unreliable memory says:
- Get a small six-cylinder engine that runs. You need alternator, starter, place to bolt the starter, water pump, fan, radiator, hoses, carb, fuel pump, small fuel tank of some sort of exhaust piping, muffler, etc.
- Build a cradle from 4x4 timbers, bolted solidly to support the rig. The usual approach was to mount it to a small trailer.
- Pick three cylinders to pump, every other one in the firing order. Remove the valve push rods from both valves on these three cylinders. Ground the plug wires for these cylinders. Remove these spark plugs. Use "non-fouling plug extenders" or plugs with the insulators removed to make adapters to fit the plug holes. To these adapters, weld/screw a pipe with a Tee fitting. One side of the Tee has a check valve so air can come into the cylinder, mounted as close as possible. The other side of the Tee has a check valve, mounted as close as possible, so that air can come out of the adapter, plumbed to the other pump cylinders and the air tank.
It helps things if you get a suitable extra flywheel and very carefully weld it to the original after cutting the center out so you can get to the original bolts. I have heard of someone using a torque converter welded shut and filled with water as extra weight, but I never saw that work. On many engines, you will need the bellhousing to mount the starter.
Probably too much trouble for most folks nowdays, but we used to be junkyard rats...
The rig will normally pump about 150 psig, volume dependent upon engine speed.
With junk yard parts, a welder and some ingenuity, you could build a portable compressor that would run anywhere for well under $75.
- Get a small six-cylinder engine that runs. You need alternator, starter, place to bolt the starter, water pump, fan, radiator, hoses, carb, fuel pump, small fuel tank of some sort of exhaust piping, muffler, etc.
- Build a cradle from 4x4 timbers, bolted solidly to support the rig. The usual approach was to mount it to a small trailer.
- Pick three cylinders to pump, every other one in the firing order. Remove the valve push rods from both valves on these three cylinders. Ground the plug wires for these cylinders. Remove these spark plugs. Use "non-fouling plug extenders" or plugs with the insulators removed to make adapters to fit the plug holes. To these adapters, weld/screw a pipe with a Tee fitting. One side of the Tee has a check valve so air can come into the cylinder, mounted as close as possible. The other side of the Tee has a check valve, mounted as close as possible, so that air can come out of the adapter, plumbed to the other pump cylinders and the air tank.
It helps things if you get a suitable extra flywheel and very carefully weld it to the original after cutting the center out so you can get to the original bolts. I have heard of someone using a torque converter welded shut and filled with water as extra weight, but I never saw that work. On many engines, you will need the bellhousing to mount the starter.
Probably too much trouble for most folks nowdays, but we used to be junkyard rats...
The rig will normally pump about 150 psig, volume dependent upon engine speed.
With junk yard parts, a welder and some ingenuity, you could build a portable compressor that would run anywhere for well under $75.
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08-20-2012, 07:59 AM
#8
Burning Brakes
17prospectivebuyer. I think the above info is correct on psi and CFM. I do a lot of blasting. I think you'll need at least 9-10 CFM at 90psi to really blast any automotive parts. Although they can advertise something that can mediablast at 4cfm you won't get very far. You can use a smaller compressor, fully charged, for small bursts of blasting. You'll get a couple minutes then need to wait for the pressure to build before blasting again. For constant blasting you need a pretty decent sized compressor. I blast anywhere from 60-80psi with a 5hp (singlestage) 80 gallon compressor. I'll keep up, but runs a lot which is hard for even a compressor this size. At some point I need to upgrage to a 7.5hp dual stage to handle the work. Try out your setup and you'll get a better feel for the equipment you'll need. But, you'll have to go much larger than what you currently have.
As for blast media, cole slag will work, but be sure to check the grit you have. I suspect you've got an 1/8th inch tip on your gun. Cole slag is generally too big for this tip size and will clog it immediately. I have a quarter inch tip for slag, but the CFM requirements for such a tip are really too big for my 5hp. cole slag is also meant to be a 'shoot to lose' media, or one time use. You can recycle it a few times before it breaks down, even get a few months out of it if you don't blast much. I'd recommend aluminum oxide or a coarse glass bead. I use both and their fine enough to be used with your tip size. They'll each last you a few months of moderate blasting before breaking down. Longer if you don't blast daily. Soda is really meant for cleaning sensitive parts. Its far, far to fine to remove paint and rust.
Blasting is a slippery slope as far as equipment goes. If you have a few small parts you want done its possible with smaller equipment. But, if you dont' want to invest in a compressor it might be easier to outsource your blasting to a local shop. They'll do a good job and it shouldn't cost you much. Good luck!!
As for blast media, cole slag will work, but be sure to check the grit you have. I suspect you've got an 1/8th inch tip on your gun. Cole slag is generally too big for this tip size and will clog it immediately. I have a quarter inch tip for slag, but the CFM requirements for such a tip are really too big for my 5hp. cole slag is also meant to be a 'shoot to lose' media, or one time use. You can recycle it a few times before it breaks down, even get a few months out of it if you don't blast much. I'd recommend aluminum oxide or a coarse glass bead. I use both and their fine enough to be used with your tip size. They'll each last you a few months of moderate blasting before breaking down. Longer if you don't blast daily. Soda is really meant for cleaning sensitive parts. Its far, far to fine to remove paint and rust.
Blasting is a slippery slope as far as equipment goes. If you have a few small parts you want done its possible with smaller equipment. But, if you dont' want to invest in a compressor it might be easier to outsource your blasting to a local shop. They'll do a good job and it shouldn't cost you much. Good luck!!
08-20-2012, 11:57 AM
#9
Rennlist Member
What Wally says is interesting. Commercial compressors such as Ingersoll Rand, etc. use eight cylinder engines to pump air for jack hammers and whatnot.
I have personally run six cylinder engines as Wally describes. Not to pump air but to time the engine. The old “time by ear” method is quite accurate if you do it correctly. Ground the plug wire to every other cylinder in the firing order. Run the engine at normal idle or as low as possible on half the cylinders. Turn distributor for maximum RPM. This will be TDC every time. Now adjust advance by turning the distributor an estimated number of degrees.
But, back to air compressors:
One cubic foot is 1726 cubic inches so a 230 CID engine has to make 7.5 revs to move 1 cubic foot (1726/230 = 7.504). Since only half the engine is acting as our compressor, it needs to turn 15 times to make 1 cubic foot of air. Given an idle RPM of 750, we would have 50 CFM (750/15 = 50) of air. PSI should equal cylinder compression so let’s say anywhere from 80 to 150 depending on the design and health of the engine used.
50 CFM at 100 + PSI is quite a bit of air so some type of bleed off or unloader valve would be required. You would probably want the smallest engine that would run on half its cylinders. A 2 cylinder would be perfect if it would run reliably.
Ideally an auto start set up run off a pressure switch would be nifty. A propane tank should work for air storage.
I say go for it 17pb.
Then again, you could just buy the proper compressor.
I have personally run six cylinder engines as Wally describes. Not to pump air but to time the engine. The old “time by ear” method is quite accurate if you do it correctly. Ground the plug wire to every other cylinder in the firing order. Run the engine at normal idle or as low as possible on half the cylinders. Turn distributor for maximum RPM. This will be TDC every time. Now adjust advance by turning the distributor an estimated number of degrees.
But, back to air compressors:
One cubic foot is 1726 cubic inches so a 230 CID engine has to make 7.5 revs to move 1 cubic foot (1726/230 = 7.504). Since only half the engine is acting as our compressor, it needs to turn 15 times to make 1 cubic foot of air. Given an idle RPM of 750, we would have 50 CFM (750/15 = 50) of air. PSI should equal cylinder compression so let’s say anywhere from 80 to 150 depending on the design and health of the engine used.
50 CFM at 100 + PSI is quite a bit of air so some type of bleed off or unloader valve would be required. You would probably want the smallest engine that would run on half its cylinders. A 2 cylinder would be perfect if it would run reliably.
Ideally an auto start set up run off a pressure switch would be nifty. A propane tank should work for air storage.
I say go for it 17pb.
Then again, you could just buy the proper compressor.
08-20-2012, 02:12 PM
#10
Three Wheelin'
Thread Starter
Very interesting depami. I never thought of timing that way. Kinda still trying to understand it actually. Can't you only use that to time on the older points systems and not the transistorized/hybrid points system used in 87- 928's? Can you explain further?
As far as air compressors:
Were you thinking of a Buick 3.8? That's 231CI (232 rounded up). How would that work with the multi-port EFI engines? How do you run an EFI engine outside of it's designated vehicle? It would be nice for it to run off of 3 cylinders, but i think it would get complex as to how you supply the proper voltage to the ECM. Are most ECM's grounded through their case or a ground wire and supplied full battery voltage? Or could get a carbureted motor and remove all the emissions crap. Then you just have to supply electricity for the ignition system.
As far as air compressors:
Were you thinking of a Buick 3.8? That's 231CI (232 rounded up). How would that work with the multi-port EFI engines? How do you run an EFI engine outside of it's designated vehicle? It would be nice for it to run off of 3 cylinders, but i think it would get complex as to how you supply the proper voltage to the ECM. Are most ECM's grounded through their case or a ground wire and supplied full battery voltage? Or could get a carbureted motor and remove all the emissions crap. Then you just have to supply electricity for the ignition system.
08-20-2012, 02:29 PM
#11
Three Wheelin'
Look around for rental- have everything ready & lots of media so you don't run out & do everthing in a day.
You won't have much success with any compressor that can run on 110v - you'll need at least a true 5hp unit with an 80 gallon tank. Unless you are going to be doing lots of blasting & painting it's
a lot of money to tie up.
This is way overkill, but if you can rent something like this for a day you can get a LOT done.
http://tucson.craigslist.org/tls/3140649478.html
You won't have much success with any compressor that can run on 110v - you'll need at least a true 5hp unit with an 80 gallon tank. Unless you are going to be doing lots of blasting & painting it's
a lot of money to tie up.
This is way overkill, but if you can rent something like this for a day you can get a LOT done.
http://tucson.craigslist.org/tls/3140649478.html
08-20-2012, 02:47 PM
#12
Three Wheelin'
Thread Starter
That would be a good way to go if you had everything you want blasted ready and disassembled. I think i might just try to rig something up either with an old engine or something else.
What about using old A/C compressors? I have one that still seals. You would have to have an oiler before the inlet and a separator at the outlet that could recycle the oil back to the oiler. I don't see why you couldn't drive it with an electric motor, weld the electromagnetic clutch to the pulley so it always generates pressure. They heat up from compression and can stand up to over 300PSI before failure, i think they could work?
What about using old A/C compressors? I have one that still seals. You would have to have an oiler before the inlet and a separator at the outlet that could recycle the oil back to the oiler. I don't see why you couldn't drive it with an electric motor, weld the electromagnetic clutch to the pulley so it always generates pressure. They heat up from compression and can stand up to over 300PSI before failure, i think they could work?
08-20-2012, 04:16 PM
#14
Three Wheelin'
Thread Starter
Ok.. but CFM doesn't relate to capacity right? CFM is what the air pump can output whenever it is on correct? Capacity would just increase the duty cycle that it comes on for right?
08-20-2012, 04:47 PM
#15
Rennlist Member
CFM (cubic feet per minute) is the volume of air moving. Essentially pump displacement X RPM. Given a fixed nozzle size of your equipment, increasing the PSI will increase the CFM and decrease the amount of time your storage tank will provide useful air.
An AC compressor will pump a 50 gallon tank up to 100+ PSI but it will take it a long time to do so, probably several hours.
That 50 gallon tank will be depleted of useful are in less than 10 minutes of blasting. Then you wait several hours for the AC compressor to pump it back up for another short run of blasting.
Your compressor should have a CFM rating at or above, preferably above, the blasters usage.
An AC compressor will pump a 50 gallon tank up to 100+ PSI but it will take it a long time to do so, probably several hours.
That 50 gallon tank will be depleted of useful are in less than 10 minutes of blasting. Then you wait several hours for the AC compressor to pump it back up for another short run of blasting.
Your compressor should have a CFM rating at or above, preferably above, the blasters usage.